Luminous discharge tube



y 1944. M. PENNYBACKER ETAL 2,354,421

LUMINOUS DISCHARGE TUBE Filed Oct. 28, 1942 T M? W 20 -uuirsn STATES] PATENT ioFF-lcli nounvous n gc l lims-rons I l 1 itzwsrzsmrmssw "to said Pennybacker Application October-rs. i942, Serial No. 8,590 I laminar-1:)- v a i This invention relates to gas discharge deof any new lamp with which itmaybe operated,

vices, such as lamps, of the hot cathode type, and relates more particularly to devices ot this character provided with internal thermostaticallyoperated starting switches and intended to be operated upon commercial lighting circuits with auxiliary ballasts or transformers whereby the voltages impressed upon the devices during striking' are of the order of 100 to 500 volts.

One object of our inyentioh is to provide a gas discharge device of the foregoing character which shall have a reasonably long life, which is capable of operation at usual \commercial volt-.

ages, and which is capable of quickeatarting and quick re-starting. These features are essential in commercially acceptable fluorescent lamps for illuminating purposes, in which held our invention ilnds particular utility.

Anotherpurpose of our invention is to provide, in such devices novel means for shielding the contact points of theinternal switching mechanism, whereby deleterious discharges between the contact points themselves, or between the hot cathode and any portion of the internal switching mechanism are prevented.

According to present practice in the art, each fluorescent lamp' is intended to beoperated in conjunction ,with a separate external starting switch. This starting switch, which is usually automatic in its action, provides a pre-heating current through the filamentary cathodes of the lamp whenever-the manual switch is closed, and

'after'a predetermined time has elapsed during which such pre-heating takes place; the switch opensthe filament circuit and substantially simultaneously a sumcient voltage is impressed across" the terminals of the, lamp in order to establish therein a self-sustaining gas discharge.

"In the typesof switches commonly employed in the art, this pre-heating of the filament and the opening of the filament circuit, if the lampv requires a higher; starting voltage than that avail? able; is followed bynre'closure of the switch and successive repetition-of the gtartlngcycle.

An abnormally high starting voltage typically occurs after 100 to 3,000 hours of 0D ration, -'and is the usualcause of lamp failure or "burn out."

If allowed to continue this repetition of the starting cycle, the switch will continue-successively to function until wear upon the elements thereof, brings about its premature destruction. Failure promptly to'remog an inoperative lamp demanding such high starting voltage, therefore greatlv shortens the effective life of the switch. An imperfect or damaged switch will the life gas ionisation due-to such ancillary disc arge interval has a. deleterious effect on the filament coating and hence on the starting voltage re- Mquired by the lamp; therefore replacement of lamp only, without replacement of switch, frequently results in shortened lamp life.

Due to n tolerances in production, and

such devices are new. i

It would be imprac c l to require users to buy them in matched pairs, and always to replace the more 'or less damaged switch whenever a lamp'replacement is made, although this procedure would result in a greatimprovement in the average life of fluorescent lamps.

to An internal starting switch, built integrally with the lamp, does more than make possible an accurately matched new switch with each new lamp. It avoids the necessity of extra parts such as the switch socket and terminals and the switch 2 ,housing required for a separate replaceable switch. It also permits the switch to be closely associated with, and directly controlled by the cathode temperature, thus providing an optimum discharge starting temperature, despite manufacw hiring variations which may occur in the characteristics of the lamp cathode, or the'associated lamp ballast. Even abnormal fluctuations of line voltages do not materially alter the filament temperature at which the herein described internal switch will open.

Prior internal starting switches have not been commercially successful because 'the'yoltages re- --quired to'start most'fluorescent lamps are sufficiently high to cause a discharge to strike between a hot cathode and a switch terminal of opposite polarity, if said terminal be exposed within theinterior, of the lampand substantially a nearer to said cathode than other electrodes of" a the lamp; The initiation of this objectionable v --di'scharge to the switch terminal is abetted by the fact that an ancillary discharge, is apt to take place between opposing ends of the filamentary electrode iust prio'r to the opening of the starting 50 switch, thus providing conditions suitable for establishing a relatively low voltage discharge inv that vicinity. While this ancillary discharge may ,be desirable in facilitating" the initiation of the main discharge in 'thelamp, yet thepresence of because either too long or too short a pre-heating tends to promote the establishment of the undesired and objectionable arc above referred to.

With the shielded or enclosed starting switch of this invention, the formation of any discharge betweenthe hot cathode and a nearby switch terminal is completely prevented, even when potentials as high as 500 volts are applied to the lamp.

In order to take advantage of the formation'of an ancillary discharge across portions of the filamentary electrode, it is possible to adjust the thermostat controlling the starting switch of this invention, so that the contact points will notseparate from one another until the filamentary electrode has reached a temperature sufficiently high to initiate such ancillary discharge.

Our invention improves upon the prior art by providing a simple and practical means of making the internal starting switch workable in discharge tubes, the relatively high starting voltage of which would otherwise cause discharge to one of the switch terminals.

Other objects and features of our invention may be understood from the following description when read with reference to the accompanying drawing, in which:

Fig. 1 is a view in side elevation of one end of the lamp, with the envelope broken away so as to show in detail the electrode and starting switch of this invention.

Fig. 2 shows the device of Fig. 1 as seen from the left side.

Fig. 3 is a schematic circuit showing one manner in which all electrodes of the lamp as well as the starting switch may be connected to an external source of electrical energy and to external ancillary devices such as an inductive ballast.

The starting switch of this invention is preferably mounted at one end of the lamp, as shown in Figs. 1 and 2. The filamentary electrode I is mounted 'so as to be stretched between support wires H and I2. Wire H is embedded in the glass press I 3, but serves only as a mechanical support for this end of the filament. Support wire I 2 is likewise mounted in the glass press and a connecting wire extends from this support wire to pin l4 extending from the lamp base 29 and serving as one of the pins supporting the tube in a socket and affording electrical connection to the interior of the lamp.

The glass press I3 is provided with an extension 15' in the form of a glass tube. From the other external pin I5, a lead wire It extends into the lower portion of tube l5, where it forms one contact point of the starting switch. The wire constituting the upper contact point I6, of this switch lies in the upper portion of the tube and emerges from the top thereof, at which point the wire is bent back reversely as indicated at H. This reverselyrbent portion has afilxed thereto by any convenient means such as welding, a U- formed bimetallic thermostat is extending toward press IS. The lower portion of thermostat i8 is mechanically and electrically coupled by means of a short length of stiff wire I! to the upper end of a second U-formed bimetallic thermostat 20. The lower end of thermostat 204s afilxed to a stiff wire 2| which in turn is welded to support wire II. This wire 2| extends in a direction parallel to the filamentary electrode and the lower end of thermostat 20 is supported thereby. Thermostat 20 is the main thermostat. It is in close proximity to the electrode l0 so as to be quickly responsive to the temperature thereof, and when heated it opens switch contacts lC-IO'. Thermostat Is is more remote from the elect o e, .4 51

opposes the action of the main thermostat 2., for a purpose later to be described.

The other end of the lamp of this invention. as shown in Fig. 3, can be formed in the conventional fashion and may include a filamentary electrode 22 connected to external supporting and conducting pins 23 and 24 at the respective ends of this electrode. Since no external starting switch is required for this lamp, pin ll may be connected by an external conductor 2! to Pin 24, located at the other extremity of the lamp. Pins l4 and 23 are connected by the respective external conductors 26 and 21 to auto-transformer 28, fed from a suitable source of electrical energy as indicated by the legend Ilflv. In lieu of employing an auto-transformer, direct connection to the power supply may be used and in series with one of the external conductors, for example conductor 21, there may be inserted, as well-known in the art, any suitable choke or ballast coil. It is to be understood that no particular method of compensating for the negative resistance characteristic of the lamp is demanded by our invention and forms no essential part of the instant invention and that in its place there may be used ballast resistors, transformers or the like, as well-known in the fluorescent lamp art.

It can be seen that while pins 23 and 24 are electrically symmetrical, pins l4 and I! are not symmetricalwith respect to their electrical connections. Therefore this lamp must be so inserted in the socket that pin ll shall be connected to one side of the source of external energy. However'if the polarized lamp be inserted in the wrong sense, electrically, into the socket, while it will fail to function normally, yet no permanent damage can result from such wrong insertion. Turning the lamp through 180 around its axis will correct wrong insertion when it occurs, or the lamp and sockets may be marked toindicate correct insertion angular positions.

It will be noted that the main thermostat 20 is placed in thermal proximity to the end of the filamentary electrode H) which latter is at all times, during normal operation of the lamp, connected through support wire I 2 and pin II to one side of the energy supply circuit. It is this end of the electrode which remains heated by the main discharge from the lamp, after the starting sequence has been completed, and in this manner thethermostatic element 20 continues to be heated, even after the pro-heating circuit has been broken by the separation of the contact points within insulating tube It is to be noted that main thermostat and compensating thermostat Ilare so constructed as to act in opposition to one another. and since they do not depend upon current flow therethrough for their operation, they may be made of comparatively low electrical resistance.

Upon closing the connections to the source of external energy, the current path may be traced as follows: through conductor 21, choke coil 2|, pin 22, filamentary electrode 22, pin 24, conductor 25, pin l5, contact wires I6 and I 6, compensating thermostat l8, connecting link wire I, main thermostat 20, support wire 2|, support wire H, filamentary electrode Ill, supportwire l2, pin l4, and conductor 28, back to the source of energy supply. -Thls wholly metallic pre-heatedcircuit causes filamentary electrodes l0 and 22- rapidly to become heated to thepoint where sufilcient electron emission for lamp operation is secured therefrom. At the same time, the heating of electrade ll causes the transfer of heat to main theristins installation in which ble.

mostat II, mainly by radiation. The operation of thermostat 20 causes the upper end thereof to move away from support wire 2|, thus raising compensating thermostat ll, lead .wire I! and therefore also raising from lower contact point It. The interruption of the circuit, at this point, causes the establishdischarge within the lamp, be-

ment of the main}. tween electrodes Ill and 22. This main discharge continues to maintain thermostatic element 20 in a heated condition. as previously explained. A's

cannot derive heat directly from filament it, it will operate in the opposite sense to that in which main thermostat 20 operates. Therefore it will tend to compensate for the rather high steady state temperature assumed by main thermostat 20 during normal operation of the lamp and will prevent too greatan open-circuit separation between the contact points l6 and i6. This means that if a lamp be turned off and then be turned on again very shortly thereafter, the thermostat II will not need to cool to the same temperature as it would necessarily be when the lamp was cold,

because compensating thermostat It has meansubstantially affected by such change of ambient temperature. This compensating action of thermostat it, while desirable in fluorescent'lamps, is by no means essential, and our invention may be constructed in a form omitting such compensating thermostat, if so desired.

In Fig. 3 there is shown no external starting switch. Such switch, if already present in an exthe lamp of this inuse may In the latter starting switch will not prevent this inventi in the circuit as a whole.

It has been found unnecessary tremely close iit between moveable contact point IO and the interior walls of tube l5, within which it moves. However it has been found desirable to make the distance between the point at which the contacts separate from one another and the upper extremity of tube "has great as possi- The greater that this distance is made. the looser can be the fit between contact I. and tube II, for a given voltage.

In order to avoid welding of the contact points,

upper contact point Ii be shorted out if so to have an exit has been found desirable to make the respective points of diflerent materials, but it has been found possible to use relatively inexpensive materials, such as copper and silver, for these con-- tact points.

In case that this invention with a single external contact pin at each end, conductor fl'may extend wholly within the tube. from one end of filamentary electrode 2!, at one end of the tube, to lead wire it at the other end thereof, with such shielding as may be required. In this case pins l5 and 14 may be dispensed with. so that there will be but a single pin at each end of the tube. Alternatively, pins II and 24 may be retained and electrically connected with the adjacent pins inside the base 2!, thus utilizing standard bases and sockets. As a further development of this form of construction, still another lead, with any needed shielding, may extend from the opposite end of filamentary electrode 22, through the length of the tube, so as to allow pin 23 to appear upon the same end of the tube as does pin it, thereby demanding the use of only a single socket in order to afford mechanical support for and electrical connection with the lamp.

While we have described our invention with reference to lamps similar to .the 30 and 40 watt commercial fluorescent lamps which start at voltages of the order of 200, it is to be understood that our invention is applicable to other lamps, and to tubes having purposes other than light- We claim: 3

A hot electrode gas discharge lamp capable of rapid restarting ii extinguished while hot, including in combination a starting device comprising a thermostat responsive to the temperature of said electrode, a switch operated by said thermostat for interrupting the pre-heatlng electric current when said electrode reaches a predetermined temperaturaand means for shielding one contact of said switch from said electrode, whereby deleterlous discharge to said switch contact is avoided, and including means for establishing a main gas discharge to said electrode upon theinterruption of said pro-heating electric current by said switc stat actim oppos tely t0 the first thermostat and relatively remote from said electrode, less responsive .to the temperature of said electrode; said switch having i s operation determined by the joint eflect of both thermostats, whereby of the gas discharge device is facilitated, and whereby said electrode constitutes x tc1111! heating element needed to operate said mus rnmzrnacm. smart-r a. nUsaEY.

it be desired to form the lamp of also including-a swond thermo so as to be 

